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Epidemiology of IBD

The peak age of onset for IBD is 15 to 30 years old, although it may occur at any age. About 10% of cases occur in individuals less than 18 years old. Ulcerative colitis is slightly more common in males, whereas Crohn's disease is marginally more frequent in women. IBD occurs more in people of Caucasian and Ashkenazic Jewish origin than in other racial and ethnic subgroups. In the past, it was thought that IBD occurred less
frequently in ethnic or racial minority groups compared with whites. But, previously noted racial and ethnic differences seem to be narrowing.

Precise incidence and prevalence of Crohn's disease and ulcerative colitis has been limited by (1) a lack of gold standard criteria for diagnosis; (2) inconsistent case ascertainment; and (3) disease misclassification. The data that does exist suggest that the worldwide incidence rate of ulcerative colitis varies greatly between 0.5-24.5/100,000 persons, while that of Crohn's disease varies between 0.1-16/100,000 persons worldwide,
with the prevalence rate of IBD reaching up to 396/100,000 persons. It is estimated that as many as 1.4 million persons in the United States suffer from these diseases.

The etiology of IBD is unknown but is thought to involve genetic, immunologic and environmental factors as evidenced by the following:

The greatest relative risk of IBD disease is found among first-degree relatives, suggesting a strong genetic component.

Smoking is one of the more notable environmental factors. Ulcerative colitis is largely a disease of ex-smokers and nonsmokers, whereas Crohn's disease is more prevalent among smokers.

Both ulcerative colitis and Crohn's disease are more prevalent in white collar compared with blue-collar occupations. It has been suggested that a work environment involving outdoor air and physical activity is protective against IBD, whereas work in artificial venues confers an increased risk.

IBD is more common in developed countries. There is a noted north- to- south variation and higher frequency in urban communities compared with rural areas. These observations suggest that urbanization is a potential contributing factor. It is postulated that this is the result of “westernization” of lifestyle, such as changes in diet, smoking and variances in exposure to sunlight, pollution and industrial chemicals.

Other factors such as diet, oral contraceptives, perinatal/childhood infections or atypical mycobacterial infections have been suggested but not proven to play a role in expression of IBD.